1. Field of the Invention
The present invention generally relates to a multiple node network and a communication method within the network. The present invention more particularly relates to a network having a plurality of terminal nodes and a management node that manages the terminal nodes and also to a communication method among the terminal nodes and the management node.
2. Description of Related Art
Computerized controls have become popular for various systems such as, for example, land vehicles and watercrafts in recent years. Components of the systems such as engines and navigation devices typically are connected with each other using a network. Such engines and navigation devices each have a terminal node on the network. A bus connects together the respective terminal nodes. A management node also is provided within the network and is connected to the bus to manage the terminal nodes.
The terminal nodes and the management node frequently communicate with each other through the bus. Generally, the bus is common to all of the nodes. In some particular transfers, two or more nodes, which simultaneously are trying to communicate, place their own frames onto the bus and a contention thus occurs between the nodes. A protocol can be provided in this communication system to arbitrate the nodes in contention. One node that wins in the arbitration only has the priority to transfer the frame. Another node that loses in the arbitration should wait until an opportunity to use the bus exists. For example, JP2001-119416A discloses a network that has such a protocol.
In such a conventional network, the nodes can use a particular frame that has at least an identifier field to communicate with each other. The identifier field can include a classification identifier or ID of each node. If two or more nodes simultaneously try to transfer the frames, the identifier field of each frame is compared with one another. In general, the respective components have different identifiers. The arbitration thus is effected and the node that has won can obtain the priority.
Watercraft, however, can employ a plurality of outboard drives such as, for example, outboard motors to propel the watercraft at significant speed. Typically, the outboard motors are controlled by the same application program because there is no reason to provide a separate communication system for the outboard motors. Drive nodes for the outboard motors thus have the same classification identifier.
Under the circumstances, the terminal nodes first transfer the frames to the management node to obtain a network address when the network is switched on. If two or more nodes simultaneously place the frames onto the bus, the identifier field of each frame is compared with one another as described above. The comparison, however, does not successfully arbitrate the contention because the identifier of each drive node is the same as one another. The arbitration thus fails. Accordingly, the network requires a large amount of time to boot up.